There are many different wireless communication systems used world-wide today, including cellular telephone systems, satellite communications, cordless telephones, short range citizen's band (CB) radio and high frequency (HF) radio systems. The communication bands and standards for many of these systems vary between applications and from for one jurisdiction to the next.
One area of particular interest in wireless communications is that of cellular telephone systems. The cellular telephone industry has been experiencing massive growth in both industrial and non-industrial countries alike. But still, a cellular telephone system in one jurisdiction may have been designed around completely different transmission frequencies and operating modes, than a cellular telephone system in another jurisdiction. Portable cellular telephones are therefore often unable to move from one jurisdiction to another.
It would be desirable to have a cellular telephone which could operate in any jurisdiction, thus being portable world-wide. However, the standards for cellular telephone technology vary a great deal. Some of the major standards are:                1. the advanced mobile phone service (“AMPS”) used in North America. This is an analog cellular system which uses a transmission frequency band between 824 MHz and 849 MHz. This band is often referred to as AMPS 800;        2. the digital mobile phone service (“DMPS”), which is used for digital communications. This system also operates at transmission frequency band between 824 MHz and 849 MHz and is referred to as DMPS 800;        3. the global system for mobile communications (“GSM”), used in Europe and Japan, which specifies a transmission frequency band between 890 MHz to 915 MHz. This digital system is often referred to as GSM 900;        4. the personal communications system (“PCS”) 1900, used in North America, which specifies a transmission frequency between 1850 MHz and 1910 MHz;        5. the Nordic mobile telephone 450 system (“NMT-450”) which specifies a transmission frequency between 463 MHz and 468 MHz, and uses FDMA (frequency division multiple access) signal modulation; and        6. the Nordic mobile telephone 900 system (“NMY-900”) which specifies an FDMA transmission frequency between 935 MHz and 960 MHz.Other communication standards are also used, and others are certain to appear over time.        
The same situation arises with respect to other communication media, such as cordless telephones. In the cordless telephone world, for example, three common standards are:                1. the cordless telephone 2 (“CT2”) standard which specifies a transmission frequency between 864 MHz and 868 MHz;        2. the digital European cordless telephone (“DECT”) standard which specifies a transmission frequency between 1880 MHz and 1990 MHz; and        3. the newer North American cordless telephones which use the industrial, scientific, medical (ISM) band, transmitting signals at a frequency band of 2475 MHz to 2483.5 MHz.        
Demand for cellular telephones and other wireless communications services is continually increasing, as is the pressure to reduce costs and increase marketable advantages such as portability and flexibility. As a result, many wireless systems are now configured to operate in more than one frequency band. However, the current technology results in multi-band and multi-standard wireless handsets and other portable devices which are expensive and bulky, and consume a great deal of power. For cellular telephones and similar consumer items, clearly, it is desirable to that these devices be fully integrated onto inexpensive, low power integrated circuits (ICs).
One of the problems is in the provision of the front end radio-frequency (RF) circuitry, and in particular, in the provision of a “low noise amplifier” (LNA). At the front end of the typical wireless device, signals received from the antenna are first fed to an LNA which amplifies the incoming signal to a level that can be handled by the rest of the receiver circuitry without introducing too much noise or distortion. Such an amplifier must have both a low noise figure and a high gain to reduce the effects of noise in subsequent amplifying and processing stages. Unfortunately, conventional LNAs or wide-band LNAs are unable to provide acceptable noise and gain performance in multiple wireless bands without unduly increasing the amplifier cost and complexity.
Most prior multi-band or multi-standard wireless receivers used separate LNAs for each of the frequency bands, or a single, multi-stage amplifier which is both complex and expensive. In either case, the size, cost and power consumption of the handset is unduly increased.
For example, a typical front-end for a multi-band, multi-standard RF receiver is presented in the block diagram of FIG. 1. Each of the input RF signals RF1, RF2, . . . RFn, is fed to a corresponding low noise amplifier LNA1, LNA2, . . . LNAn which is optimized for the particular frequency, amplitude and other characteristics of the input signal RF1, RF2, . . . RFn. Each amplified signal is then fed to a direct conversion element DC1, DC2, . . . DCn, or some other manner of signal demodulator, which converts the amplified signal to a lower frequency for processing or filtering. Typically, the RF signals are demodulated to an “intermediate frequency” (IF), or to baseband (the frequency of the original signal. In the case of voice communications, for example, the baseband would be audio frequency).
Clearly, this is an inefficient way of providing a multi-band or multi-standard receiver. The large number of components makes for a physically large, expensive, high power consuming, and unreliable device.
The continuing desire to implement low-cost, power efficient receivers has proven especially challenging as the frequencies of interest in the wireless telecommunications industry (especially low-power cellular/micro-cellular voice/data personal communications systems) have risen above those used previously (approximately 900 MHz) into the spectrum above 1 GHz. Attempts to provide flexible designs in Radio Frequency Integrated Circuits (RFICs)—also known as monolithic microwave integrated circuits (MMICs)—allowing for multiple standards and varying conditions of reception have met with limited success. These designs usually provide this functionality by means of multiple, independent signal paths—one signal path and set of components for each frequency standard and/or set of operating conditions. This is an expensive and physically bulky approach which suffers from all of the performance problems described above.
Thus, there is a need for a simple and inexpensive low-noise amplifier which can operate in at least two distinct frequency bands, addressing the problems above. It is desirable that this design be fully-integratable, inexpensive, physically small, power-efficient, reliable, and high performance. As well, it is desirable that this design be easily applied to multi-standard/multi-frequency wireless applications.